Low amplitude audio frequency switching system



Nov. 10, 1942. w. J. MORLOCK 2,301,224

LOW AMPLITUDE AUDIO FI QEQUENCY SWITCHING SYSTEM Filed April 29, 1941fiemwaza m/rzz J Q ar-- J! H 6/ 1 l i l ms. mm

Patented Nov. 10, 1942 UNITED LOW AMPLITUDE AUDIO FREQUENCY SWITCHINGSYSTEM William J. Morlock, Indianapolis, Ind., assignor to RadioCorporation of America, a corporation of Delaware Application April 29,1941, Serial No. 390,930

7 Claims.

This invention relates to low amplitude audio frequency switchingsystems. More particularly, the invention relatesto a relay system fortransferring or switching low amplitude or low level audio frequencysignal conveying circuits by remote control.

Low level audio frequency circuits, as referred to herein, may include aplurality of microphone or photocell signal pickup circuits and thelike, which operate at extremely low audio frequency level and whichconvey no appreciable current or voltage.

As such circuits operate at extremely low audio frequency signal levels,they are normally connected to high gain amplifying means for converting the signal from a source into a signal of useful magnitude.Accordingly, such low level circuits are sensitive to hum and noisesignal pickup, and transfer or switching means employed therein mustprovide low resistance and stabilized connections involving low andconstant contact resistance under all conditions of operation, even whenthe switching or transfer means is subjected to extreme vibration.

Because of the universal availability of the supply, it is desirable,and is present practice, to operate relays and other remote controlswitching means with alternating current. However, when used to energizethe relay coils for transferring or switching low amplitude level audiofrequency circuits, such as microphone and photocell pickup circuits,considerable difficulty has been encountered heretofore because of (1)pickup of alternating current voltages from the relay coil circuit, (2)pickup of stray voltages from the supply leads to the relay operatingwindings or coils in close proximity to the audio frequency conveyingleads connected with the relay contacts, (3) lack of sufficient slidingor wiping contact in the switching means to prevent an appreciable orVariable contact resistance and with no contact voltage sufficient tobreak down the contact resistance, and (4) contact vibration whensubjected to shock or vibration, as in gun-fire control systems and thelike, or in rapidly moving vehicles.

It is, therefore, a primary object of this invention to provide animproved low amplitude level, audio frequency transfer or switchingsystem adapted for remote operation, which substantially preventscontact vibration and stray voltage pickup from the operating circuits.It is also an object of the invention to provide an improved relay orswitching device which is simple and long periods of time and underadverse operating conditions including extreme vibration.

It is a further object of this invention to provide a low level audiofrequency relay 0r circuit switching means which is adapted foralternating current operation and the switching control of lowamplitude, level audio frequency circuits, without complicated wiringconnections thereto, while substantially eliminating stray hum voltagepickup.

It is a still further object of this invention to provide an improvedrelay or circuit switching means for low amplitude level audio frequencycircuits which is adapted for multiple operation in groups, whileelectrically isolating or shielding the operating and controlledcircuits whereby alternating current may be used for energizing theswitching means.

In accordance with the invention, a relay or switching device isprovided with a base plate of conducting material, such as sheet metal,of such size that it is adapted to form a closure for an opening in agrounded shield wall extending between the controlled audio frequencycircuits and alternating current operating windings for the switchingmeans, thereby permitting a plurality of such devices to be utilized ingroups in or on a metal panel of a control apparatus.

dependable in construction and operation over In order that theinvention may further be understood, attention is now directed to theaccompanying drawing and the following description, together with theappended claims.

In the drawing, Figure l is a front view of a relay or switching meansin a system embodying the invention,

Figure 2 is a side view thereof, both views being substantially fullsize, and

Figure 3 is a schematic circuit diagram of a relay or switching systemembodying the invention and provided with a plurality of relays orswitching means as shown in Figures 1 and 2.

Referring to Figures 1 and 2, 5 is a grounded panel of an apparatusinvolving a plurality of low level audio frequency circuits for whichsuitable circuit transfer or switching means is provided. lhe switchingmeans comprises a metal base plate 6 adapted to fit over a panel opening1 with a relay-operating coil 8, core 9, and armature l 0 on one sidethereof, and with movable and fixed insulated contact means on theoppoing terminal members [5 secured to an insulating plate l6 mounted onthe base 6.

The contact means further includes two pairs of opposed laminated springcontact fingers and 2| forming extensions of two insulating arms 22 and23 secured to a metallic spacer block 24 pivoted to rotate about a pivotpin 25 which extends through the block 24 and two supporting brackets26, also mounted on the insulating plate The pairs of contact fingersare connected to terminals 28 which,in turn, are connected throughflexible leads 29 with base terminal members 30. As will be seen, thecontact arrangement of the present example provides a double-pole,doublethrow switch means, although any other suitable contact orswitching arrangement may be provided wherein one or more pairs oflaminated contact fingers 2ll--2 I, are pivotally mounted, and insulatedto move directly from one contact to another with a sliding or wipingaction, the contact engaged being in the plane of movement of thecontact fingers and being blade-like and gripped'on each side by thecontact fingers.

The operation of the contacts is provided through a mechanical link orrod which extends through a small opening 36 in the shield plate or base6, between a pivot pin 31 in the switch lever base 24 on the oppositeside of the pivot 25 from the contacts 2il2l, and a pivotal connection38 at one end of the armature ill. A coil spring or other suitabletension means 39 surrounds the link 35 and presses against the end ofthe armature II] and the end of the block 24 to take up any play in thebearings about the pivot axes 25, 3'! and 3B.

The armature is positioned with one end adjacent the pole piece 40 ofthat portion of the core 9 which extends through the coil 8, while, atan intermediate point between the pivot connection 38 and the portionopposite the pole piece, the armature is pivotally mounted as indicatedat 4| between a pair of frame members indicated at 42, which serve toclamp and hold the core. A retracting spring 43 is connected between thearmature and a fixed connection 44 on the frame 42 to withdraw thearmature from the pole piece 40 and against the inner end of a stopscrew 45 which extends through the base plate 6 and the insulating basel6.

By adjusting the screw 45, the armature It] may be positioned, with thewinding deenergized, to move the switch lever and the contacts 2ll2linto proper alignment with the contacts ll-IZ as shown in Fig. 2. Whenthe coil 8 is energized the armature is attracted, causing movement ofthe lower end and the pivot connection 38 to the left, therebytransmitting a corresponding movement to the pivot connecion 31 on theswitch lever means and causing the contacts 202l to move to the rightinto engagement with the contacts |3l4.

The same coil terminals and connections may be provided in any suitablemanner, one terminal being indicated in Figure 2, at 48, to which a leadwire 49 is connected. The lead wire 49 extends from the coil 8 along acasing wall 50 for the apparatus which is in spaced relation to thepanel or wall 5, forming a compartment within which is located theoperating magnet or motor means 8 and the alternating current supplycircuit connections therefor. On the opposite face of the wall or panel5 where is provided the,signal carrying and controlling contacts of theswitch means and the connection leads therefor indicated at 52, theseleads being broken in Figure 2 in order to show the construction of therelay device more clearly.

With this arrangement, it will be seen that the operating or free endsof the armature and switch means provide a relatively wide range oftravel, while the link-connected opposite ends move through a relativelyshort distance. The armature and switch arms are arranged forsubstantially parallel operation on opposite sides of the shield wall 5.This arrangement has the further advantage that it overcomes thedisadvantages encountered in previous designs and enumeratedhereinbefore. The operation of the contacts is accomplished wholly bymeans of a mechanical link through a small opening in the shield plateor wall at a point substantially remote from the contact end of theswitch means.

This arrangement permits the coil or operating windings 8 to beenergized from any suitable alternating current source, while beingentirely shielded from the low level audio frequency control contacts,as the metal base plate 6 forms, when mounted, an integral part of theshielding main panel 5 of the apparatus. Therefore, it will be seen thatthe wiring to the relay coil or coils, where a plurality are mountedupon a single panel in a group, may be located on one side Of the panel,while low level audio frequency wiring for the contacts may be locatedon the opposite side of the panel.

Furthermore, this arrangement in the switching means provides foreliminating the difficulty hereinbefore experienced in keeping lowvoltage contacts sufiiciently clean to function properly. Because of thepressure exerted on each side of the stationary contact by the pairs ofcontact arms 20 and 2!, a continuous sliding or wiping contact isprovided, which serves to remove dirt or corrosion ahead of the movingarm, instead of compressing and holding it as in conventional types ofrelays.

Accordingly, the contacts wipe clean as they operate and do notintroduce into the circuit any appreciable contact resistance which, inhigher voltage relays, is normally broken down by the applied voltage.In low level audio frequency circuits, as hereinbefore mentioned, thereis no appreciable transfer of current or voltage through the circuit orcircuits connected with the relay.

Additionally, the construction shown and described overcomes the contactvibration hereinbefore considered, for the reason that relatively longcontact arms are normally free to vibrate at the contact end, whereas,in the present arrangement, the movable arm is damped and held in placeby the gripping action of the contacts on each side of the fixedcontact. The friction at the free end of the movable contact means, plusthe restoring spring pressure, is sufiicient to keep the relay contactsfrom changing position during a heavy shock or in the presence ofvibration. It is, therefore, highly desirable for use in connection withgun-fire control circuits and the like.

Referring now to Figure 3, along with Figures 1 and 2, the panel 5 ofthe apparatus is indicated schematically with the contacts of severalrelay or switch devices schematically indicated at 80, BI, 62 and 63 forfour relay devices, the operating coils of which are indicated on theopposite side of the panel 5 at 64, 65, 66 and 61. Each coil is providedwith an operating armature 68 connected as indicated with the contactsfor which the operating coils are provided. To minimize electricaldisturbances in the control circuits, each relay coil may be providedwith a shunt capacitor .69.

Each relay device serves to connect a low level signal input circuit,such as microphone circuits 10, with an audio frequency output circuitII, which is connected through a preamplifier system 12 and a poweramplifier 13 to an output bus circuit 14 to which suitable outputdevices, such as loudspeakers 15, may be connected as indicated.

The microphones 16 connected with the leads 70 are provided each with acontrol button or suitable switching means 11, I8, 19 and 80, forcontrolling the relays and the connection of the respective microphoneto the output line H. In the present example, the relay coils 64-61 areenergized from alternating current supply leads BI and control leads 82connected with the con trol buttons 18--80 as shown, whereby controlbuttons 18--80 serve to operate the coils or relays 6461, respectively.

It will be noted that the microphones may be extended to suitable remotepoints, while the control is centered at one point in such a manner thatthe audio and operating circuits are isolated by the shield wall 5. Itis also desirable that the leads and H be shielded as indicated by theshield connections 82.

In a system as shown in Figure 3, it has been found that switchingoperation of relatively low level audio frequency circuits in connectionwith high gain amplifier devices, as at 12 and 13, is highlysatisfactory, being substantially without hum pickup as ordinarilyexperienced with control circuits of this type when groups of relaymagnets are operated with alternating current.

The contacts are preferably silver plated on the operating surfaces andhave been found to have an operating life of several hundred thousandoperations. A thin lubricant of petrolatum and zinc dust for the contacthas been found to extend the operating life considerably withoutaffecting the electrical operation or contact resistance.

I claim as my invention:

1. The combination with a control panel having a switch opening, of ashield plate adapted to provide a closure for said opening, a pivotallymounted switch member on one side of said plate comprising a pair ofopposed spring contact fingers and a fixed contact blade engaged onopposite sides by said fingers, means for moving said fingers out of andinto gripping engagement with said blade comprising a pivotally mountedarmature on the opposite side of said shield plate, means providing asingle opening in said plate, a link member extending through saidopening and connecting said armature and switch member, electromagnetmeans for actuating said armature, and spring means for retracting saidarmature with respect to said electromagnet means.

2. A relay operated low level audio frequency switching device having anoperating winding, a magnetic core and an armature associated with saidWinding, a switch comprising pivotally mounted spring contact fingersand a fixed contact blade engaged by said fingers, means providing ametallic shield wall interposed between said switch and said operatingWinding, and a link connection extending through said shield wallbetween said switch and armature for mov- 3. A low level audiofrequency'lrelay switch comprising in'combination, a grounded shieldWall having a removable portion providing a base plate, a pair ofopposed spring contact members, pivotal mounting means for said memberson one side of said plate providing movement of said members in pairs, afixed switch contact blade engaged on opposite sides by said contactmembers, means for moving said contact elements into and out ofengagement comprising a pivotally mounted armature on the opposite sideof said base plate and a link member extending through said base plateand connecting said armature and pivotal mounting means, and analternating current winding for actuating said armature.

4. A low level audio frequency relay switch comprising in combination, ashield plate adapted to provide an apparatus shield cover, a pivotallymounted switch member having an arm carried thereby, a pair of opposedspring switch contact members forming an extension of said arm, a fixedswitch contact blade gripped on opposite sides by said contact members,alternating current motor means for moving said contact members out ofand into engagement therewith comprising a pivotally mounted armature onthe opposite side of said shield plate, and a link member extendingthrough said shield plate and connecting said armature and pivotallymounted switch member.

5. A low level audio frequency relay switch comprising, in combination,a grounded shield wall having a removable portion providing a baseplate, a pair of opposed spring contact members, pivotal mounting meansfor said members on one side of said plate providing movement of saidmember in pairs, a fixed switch contact blade engaged on opposite sidesby said contact members, means for moving said contact elements into andout of engagement comprising a pivotally mounted armature on theopposite side of said base plate and a link member extending throughsaid base plate and connecting said armature and pivotal mounting means,an alternating current winding for actuating said armature, and lowlevel audio frequency terminals connected with said contact members onthe opposite side of said base plate.

6. A remote control system for low level audio frequency signalconveying circuits comprising, in combination, a plurality of low levelaudio frequency signal conveying circuits, alternating current controlcircuits for said system, a metallic shield wall interposed between saidsignal conveying and control circuits, a pair of opposed pivotallymounted spring switch members connected with certain of said signalconveying circuits on one side of said wall, a fixed switch contactblade engaged on opposite sides by said members, means providing aconnection with said contact members for one of said signal conveyingcircuits, alternating current motor means for moving said contactelements out of and into engagement comprising a pivotally mountedarmature on the opposite side of said base plate and shield wall, and alink member extending through said base plate and connecting saidarmature and pivotal mounting means for said contact members, said motormeans including a winding connected with one of said control circuits.

7. A remote control system for low level audio frequency signalconveying circuits comprising,

in combination, a plurality of low level audio frequency signalconveying circuits, alternating current control circuits for saidsystem, a metallic shield wall interposed between said signal conveyingand control circuits having a removable portion providing a base plate,spring contact members connected with certain of said signal conveyingcircuits on one side of said wall, pivotal mounting means for saidmembers carried by said base plate, a fixed switch contact blade engagedby said contact members, means providing a connection with said contactblade for another of said signal conveying circuits, alternating currentmotor means for moving said contact members out of and into engagementwith said blade comprising a pivotally mounted armature on the oppositeside of said base plate and shield wall, a link member extending throughsaid base plate and connecting said armature and pivotal mounting meansfor said contact members, said motor means including an alternatingcurrent actuating winding connected with one of said control circuits, alow level signal pickup device connected to one of said signal conveyingcircuits, and means for applying an alternating current to said Windingthrough on of said control circuits.

WILLIAM J. MORLOCK.

